A variety of aqueous coating compositions comprising epoxy resin and acrylic polymer are known in the art and several are commercially available. In order to obtain desirable characteristics for many critical end use applications, such as coatings for sanitary cans, it is considered necessary to include a high proportion of epoxy resin in the composition. Epoxy contents of 60 to 80 percent are commonly used. Typical epoxy acrylate compositions are disclosed in U.S. Pat. No. 4,247,439 to Matthews and Sommerfield; U.S. Pat. Nos. 4,212,781 and 4,308,185 to Evans and Ting; and U.S. Pat. No. 4,302,373 to Steinmetz; all of which are incorporated herein by reference.
U.S. Pat. No. 4,285,847 to Ting discloses epoxy acrylic compositions in which the epoxy acrylic is made by free-radical grafting of ionizable side chains onto an epoxy backbone; dispersing this product in water and thereafter polymerizing, in situ, addition polymerizable monomers which may or may not also contain ionizable groups. By this means the solids content of the composition is increased and the proportion of total epoxy resin in the composition is reduced by replacement with the cheaper addition polymer thereby reducing the cost of the composition.
In accordance with the present invention cost reduction as well as several other advantages over U.S. Pat. No. 4,285,847 are obtained. By using an epoxy acrylate prepared by an esterification reaction between epoxy resin and acrylic polymer instead of the graft epoxy-acrylic of U.S. Pat. No. 4,285,847, benefits are obtained in the latitude of solids and viscosity which can be conveniently obtained, and in the ability to reduce the amount of amine neutralizing agent necessary to obtain stable water dispersions having useful viscosity. These and other advantages will be apparent from the following disclosure.